Yolanda Foster Lyme Disease: Lisa Vanderpump Unsure Of 'RHOBH' Co-Star's Diagnosis [VIDEO]

Lisa Vanderpump is unsure of Yolanda Foster's Lyme disease diagnosis.

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Although the reality star and restauranteur didn't come right out and say that her Real Housewives of Beverly Hills co-star was faking her illness, she admitted to having a few questions about the authenticity of Foster's diagnosis during filming on season six.

“I don’t quite understand what’s wrong with her,” Vanderpump said during a confessional, according to a report by Us Weekly on Monday. “I don’t know if it is Lyme disease, but I’m not criticizing her. I’m just questioning it.”

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Foster claims to have been diagnosed with Lyme disease in 2012, around the time she joined The Real Housewives of Beverly Hills as a full-time housewife for season three.

“She was having some anesthetic, she had a stem cell transplant — just a lot of stuff,” a confused Vanderpump was seen telling Kyle Richards as the clip continued.

The cameras then go to Foster, who explains her health journey during a confessional of her own.

“You know it’s been a journey. I look quite normal, but yet I’m so sick,” she said. “I have weakness in my legs, no brain function — I mean, I haven’t driven a car in three years... Its been like trying to uncover a murder mystery.”

For more of Lisa Vanderpump and Yolanda Foster, tune into The Real Housewives of Beverly Hills' sixth season, premiering on Tuesday, Dec. 1, at 9 p.m. on Bravo.